Anticonvulsants are the standard treatment for epilepsy, but only control the symptoms without addressing the mechanisms of the disease. About 1/3 of patients develop drug-resistant epilepsies and only some are candidates for resective surgery as a final attempt to reduce seizure occurrence. Recently, our laboratory has pioneered the characterization of inflammatory cell infiltrates in surgically removed fresh brain samples in a search for novel therapies that may target the cause of epilepsy. Our data strongly indicate a role for immune cell activation in the epileptic brain irrespective of the particular etiology of epilepsy. We discovered significant brain infiltration of functionally activated lymphocytes in both epileptic patients and experimental animals. Additionally, steroids that are known for their anti-inflammatory properties have shown efficacy in a number of types of drug-resistant epilepsy. However, the profound immunosuppressive and other severe side effects of chronic steroid use have prevented widespread prescription of these drugs to otherwise treatable patients. The goal of this proposal is to use mouse models to design novel therapies to treat epilepsy using directed immunomodulatory approaches independent of broad-acting immunosuppressive agents. We propose to test the hypothesis that dampening ongoing inflammation in the brain could effectively reduce epileptogenic effects of early-life seizures and ultimately prevent epilepsy in the absence of systemic immunosuppression. This proposal has two aims. Specific Aim 1 will determine the efficacy and underlying mechanisms by which biodegradable nanoparticles formulated from the FDA-approved biopolymer poly(lactide-co- glycolide) (PLG) induce leukocyte sequestration in the spleen and reduction of brain inflammation to prevent the priming effect of early-life seizures. Specific Aim 2 is designed to assess the efficacy of autologous natural regulatory T cell (nTreg) infusion and the potential synergistic effect of PLG nanoparticle treatment in combination with exogenously introduced nTregs in the amelioration of neuroinflammation in murine models of epilepsy. Our previous work documented the success of using biodegradable nanoparticles to treat a variety of inflammatory immune-mediated diseases in animal models. Strikingly, our preliminary results indicate that treatment with PLG nanoparticles can improve seizure outcomes in our two-hit model of epileptogenesis. We propose to elucidate the underlying therapeutic mechanisms. Additionally, we propose to test the ability of a patient's nTregs to dampen immune responses in the epileptic brain alone or in combination with PLG nanoparticles. We have previously reported that supplementation of nTregs could significantly reduce disease severity in several animal models of multiple sclerosis by preventing brain inflammation. Our approaches that target inflammation and restrict brain infiltration by inflammatory leukocyte subsets in the absence of the complicating effects of steroids are highly novel and may be a major step forward for the translation of novel treatments for the root cause of epilepsy.